Erebos, Bleak-Hearted is the most important card in the deck. Erebos acts as the most consistent draw engine. Erebos is also the biggest creature in the deck once 5 devotion is hit, along with being quite difficult to remove. Erebos also protects again boardwipes, as you can pay life to refill your hand after a boardwipe. Erebos's activated ability also deals with small indestructible creatures such as Brash Taunter and Toski, Bearer of Secrets.
Ayara, First of Locthwain is another useful draw engine along with contributing three black devotion and gaining life. Ayara will commonly sacrifice Eyetwitch, Mire Triton, and the token from Inkling Summoning. Ayara is unable to sacrifice the white goat token created by Woe Strider.
Woe Strider is a good all-around card. Woe Strider performs very well against Dimir Rogues and removal cards due to its escape ability. Mire Triton puts cards in the graveyard to help Woe Strider escape. The token Woe Strider creates cannot be sacrificed by Ayara, First of Locthwain, but it can be used by Woe Strider, Erebos, Bleak-Hearted, Village Rites, and Eradicator Valkyrie.
Eradicator Valkyrie is the biggest source of life gain and the strongest flyer in this deck. Its boast comes in handy to force opponents to sacrifice good creatures. The two devotion comes in handy for Erebos, Bleak-Hearted and the hexproof from planeswalkers is occasionally helpful. While I originally ran Rankle, Master of Pranks as it is the same mana cost and a bit more versatile, Eradicator Valkyrie's lifelink has proven to be very useful, especially with how often I draw using Erebos, Bleak-Hearted's passive ability.
Mire Triton acts as a graveyard filler and a very good defender due to its deathtouch. It can also act as a sacrifice target if necessary.
Eyetwitch is a great turn-one play and a very good sacrifice target. Its learn ability is very useful as it allows you to get a useful card depending on the situation.
Village Rites provides decent card draw for very cheap and at instant speed. Village Rites is most useful when an opponent casts a removal spell, as you can sacrifice the targeted creature in response, essentially drawing two cards for one black mana. This will also cause adventure removal spells like Murderous Rider, Bonecrusher Giant, and Giant Killer to fizzle. Village Rites is also good when chump blocking.
Bloodchief's Thirst acts as good early removal and alright planeswalker removal. This card is in the deck mostly to deal with Hallowed Priest and Ruin Crab.
Heartless Act is decent versatile creature removal at instant speed.
Agadeem's Awakening
will generally be cast as a land in the early game. In the late game, Agadeem's Awakening can be cast for X=4, allowing the return of up to 4 creatures, which can be great against Dimir Rogues and mill in general.
Castle Locthwain is just a backup draw method. With 16 Swamps in the deck, this will come into play untapped almost all the time.